Acidification of aquatic and terrestrial ecosystems in the
northeast United States due to increased atmospheric acid
deposition has been a significant environmental problem for over
60 years. Amphibians are particularly vulnerable to acid
precipitation due to their aquatic breeding habits and permeable
skin. Low pH affects amphibian larval growth rate, embryonic
development , distribution in both aquatic and terrestrial
habitats.

Intraspecific variation and the possibility of adaptive evolution
of amphibian populations in environments of different pH remain
largely unexplored. These questions are all the more important in
assessing the possible relationship between acid deposition and
amphibian decline.

The red-spotted newt Notophthalmus viridescens is
widespread in eastern North America. In southern Vermont, this
salamander is found in ponds with a wide range of pH. My students
and I have been studying six populations of newts from ponds of
very different pH. The high pH ponds are in the foothills of the
Taconic Mountains which are underlain by extensive limestone
deposits. These ponds have had an average pH of 8.1 over the past
four years. The low pH ponds are in the Green Mountain Plateau,
with a granitic base with little buffering capacity. The average
pH of these ponds has been 4.6 over the last four years.

The populations from these two groups of ponds provide an
opportunity to investigate whether the newts have responded
evolutionarily to different pH environments. Given that the pH of
precipitation in the northeast has been low for over 60 years and
given that newts exhibit fidelity to their natal ponds, it is
likely that populations from different mountain ranges have been
isolated in ponds of different pH for many generations.

For several years my students and I have been asking whether pond
pH has served as a selective agent in the evolution of newts. Two
questions are at the center of this research: